Retractable landing gear



Dec-'9, 1947- c. s. GLASGOW Erm.. 2,432,408 Y RETRACTABLE LANDING GEAR Filed Dec. '1. 1942 5 sheets-sheet 1 v 15a/ward E urfan /mr/eff/afgon/ F E421- mmm ATTORNEY D69 9, 1947- c. s. GLASGOW Er AL 2,432,408

` RETRCTABLE LANDING GEAR Filed- Deo. '7, 1942 5 Sheets-Sheet 2 Char/eff G/cz/gon/ j INVENTOR,

` ATTORNEY ec. 9, 1947. c. s. GLAsGow Er Al. 2,432,408

RETRACTABLE LANDING GEAR lf'led Dec. 7. 1942 5 Sheets-Sheet 3 INVEN'IDR.

, BY ATTURNEY Dec- '9 1947- c. s. GLASGOW ET AL 2,432,408

RETRACTABLE LANDING GEAR Filed Dec. 7, 1942 5 Sheets-Sheet 4 plg. H. Edward /f' Bur/0n INVENTO BY Qm www Arme/m Deug, i947.

c. s. GLASGOW l-:r AL RETRAGTABLE LANDING GEAR 5 ,Sheets-Sheet 5 Filed Dec. 7. 1942v W MR w #M m M6 f5 ,05 rf al. ,WW f/M E L .iw BY am Patented Dec. 9, 1947 "Edward BurtonfLos Angeles, Calif., assign- -ors to Douglas l'iiir'craft .Gompanm` \Inc.-,L Santa Monica, Calif.

.Application December 7, 1942, SerialNo. 468,304

17""Claims. (Cl..244'-102) 1-1 VThis invention relates toa retractable landing 'gear for*` aircraft. It is especially applicabledo afmain landing .gear (for relatively'lfieavy .airplanes.

It is `one object -of theiinvention ,to.providefa lan'ding gear which maybe ,extended from the compartment in the nacelle or ,other .part of .the airplane into landingpositionunder emergency conditions .by the dynamica-etion of `therelatively 'moving air stream. `.A landinggearis normally retracted into itshousing compartment and extended therefrom by powermeans, usually a hydraulic jack. .Should this power means fail, alanding gear of this invention is .readily and rapidly extend-ed by the action `of :gravity and ofwind load. m

.Itis another object of the invention to provide a stu-rdily constructed locking mechanism for 4securely xing the relatively moving parts `of the landing gearinextended landingposition It .is-a further 4object to provide such alockin'g mechanism which will automatically lock the gear `when it assumes the fully-extended positionand additionally va locking mechanismowhich is locked andr released by the same power `means which effects the extension and retractioncofuthe gear.

YItis an object of the inventicnrto;providexan efcient .bungee `device which .iwi-ll" apply `-afftresilient forceY to the relatively 4moving par'tsfofthe i landinggear tending to move them toeXtended landing position. Assurance of extension `iofiftlfie landing gear is thereby increased, the fbung'e'e laiding the power means: under-.normal "conditions andi-augmenting the action of gravityandw'ind resistance when the power means partially or Wholly fails. It is a' further object ofthe'invention to pr-ovidefan arrangement v of "a bungee 'devicewhich `will act upon both the folding links stroke*butv of'4 a "generally-y uniforml and moderate Value.

In=the==absence of f'alocking latch, when: the gear is fully retracted, the hydralllicjackisthe only #means f acting to hold I"the figear yin --its retracted' position. -`I`f the *load-stroke `curve f for retraction and extension terminatesfat theretra'c'tion *end* with'a4 relatively lowf load value; it is apparent ithat y"the llinkage, `of which Asuch a curve l'git/'es' "the performancel character, Voperates to enable the hydraulic jack to hold the gear n"'fu-l"ly"retracted position-at a relatively high mecnanicalradvantafge. =It"is" therefore "a further :object of 'i this invention to "provide f 'an "arrangeiner1t=-ofthe4 hydraulic; jack' and linkage connecting the aircraft'structure" and main wheel carryingstrut' which willaiord ua `loadfstrok'e curve 'in whichtheiioa'd'will be relatively'light. atthe retraction endpftthetcurve.

""tlrr'd'er some conditions `|'confronting 1a "designergav dua'lwvhe'el .gear isindic'ated pas 'preferable to asingle wheel construction. Two small Wheelsfmayjbe less expensive, .more practicable and moreeasil'y procurablethan vone large-wheel 25 for 'aj'gi'ven loadrequire'ment, especially thegreater loads to whichthelandinggeartffalarge airplane is subjected. '.,Itis antobjectiofthe-invention-to .providea retractinglinkagewhich will, in '.the retracted position, occupy rthe .space Hbetween the twowheels cfa-.dual zwheelgear, `thus combining rthe ...advantages-.of the 'dual wheel constraiction--Withztheadvantage of `a compact arrangement of the retracted landing-gear, *reducingthe size ofithe nacelle compartmentf'and flessening themeight of= the gear.

:It 1 is astill another frobject: of 'i the invention to provideiadoorfclosingvdevice. .for the 'landing :gear

compartment fina-the .nacelle-which L is; controlled by the movingsgpaittsfiofi the l.gear withieiciency reliabilitysecurity andl withoutfsla'p either duringcoperative'movements forwhile in closed position.

- Otheryobjectszand advantageswill appearr'om atreadingiofr thefollowing-rdescription and claimsl Figure 4 is a perspective view of the landing gear in its fully extended position;

Figure 5 is a perspective view of the landing gear similar to that in Figure 4 showing the gear in a fully retracted position;

Figure 6 is a sectional elevation taken through the landinggear and nacelle showing the door operating mechanism in the open positionr while the landing gear is extended;

Y Figure 7 is a sectional elevation taken through the landing gear and nacelle similar to that, shown in Figure 6 showing the door operating mechanism and landing gear in 'the retracted position;

Figure 8 is a plan View of the nacelle doors in the closed position showing their general arrangement;

Figure 9 is a perspective view of the landing the arms 46 of the upper links 26 when the links 22 and 26 are in extended position.

Arcuate recesses 62 formed at the outer ends of the arms 63 receive the shaft 6D carried between the arms 46 and act as a stop therefor when the links 22 and 26 are in extended position,preventing the drag links from moving outwardly past their position of longitudinal alignment. Outwardly as used herein in connection with the break links refers to that side of the links which trails in the folding movement of gear retraction.

A latch arm 58 pivoted to the shaft 60 is provided with a finger 'H at its outer end arcuately contoured on its inner face to engage the pivot shaft 28. The inner face of the finger 'H serves as a stop to limit movement of the latch arm 58 when the plunger 44 is retracted. A

gear locking device shown in the locked .position;

Figure 10 is a sectional view of the locking mechanism in the locked position showing the drag links in solid lines and the locking latchjin phantom Y lines;

, Figure 11 is a sectional view similar to Figure 10 showing the locking mechanism in the unlocked position;

Figure 12 is a section taken through the inner retracting link showing the arrangement of fluid Vpassages therein leading to the hydraulic jack.

`In detail and with reference to the accompanying drawings, Figures 1, 2 and 3 schematically show a shock strut I8, the shock absorbing operation of which is well known in the art, and which `is pivoted to a shaft l2 VmountedV on the airplane frame structure 3|. A piston plunger I4 of the shock absorber of the strut carries a collar I6 to which is secured an axle I8 upon which dual pneumatic wheels are mounted. The retracting linkage comprises a pair of upper break links 26 anda pair of lower break links 22 the latter being cross bracedto form a single rigid member. The links are hinged together by a shaft 28. The lower link is pivoted at its lower` end 24 to the shock strut. The upper ends'of the break links 26 are pivoted to. a shaft 35 mounted on the airplane structure 3i.

A pair of outer retracting link arms 32V are pivoted by means of a shaft 34 to the upper break links on an axis which is adjacent the pivot shaft 36.V The opposite ends of the arms 32 are vpivoted to a pivot shaft 36 to which is also pivoted a hydraulic strut or jack 42 and additional retracting link arms 38 which are in turn pivoted to the airplane structure 3l by a pivot shaft 40. A piston plunger 44 of the hydraulic strut 42 is pivoted to a shaft I2 carried between extension arms 46 on the upper break links 26 in a manner presently to be described.

In order to keep the axle carrying collar I6 and the piston I4 from turning with respect to the shock strut Il), the usual upper and lower torque links 48 and 50 are provided .which are pivoted together at 52, the upper torque links being pivotedV to the shock strut at 544 and the lower links to the axle carrying collar I6 at 56.

`As shown'in Figures 4, 5, 9, 10 and l1, a locking mechanism is supported between extension arms 46 of the upper drag links 26. When the landing gear is in its fully extended position, the break links 22 and 26 are in a longitudinally aligned relationship. The unper ends of the lower break links, have arms 63 extending laterally outwardly therefrom ,in overlapping relation-with lug 64 is formed on the inner face of each of the lower drag link arms 63, which is adapted -to engage one of two similar lugs 66 provided on the latch arm 58 when the latch arrn is rotated to the right. A semi-circular guide flange 68 concentric with the shaft 28 is provided on the inner `face of each of the lower drag links. This flange is spaced from the shaft and forms therewith a groove 13 adapted to receive and guide a lug 'I8 carried by the latch arm 5B.

As the piston of the plunger 44 is pivoted with the pin l2 carried by the latch arm 58, continued movement of the plunger to the right, as viewed in Figures 9, 10 and 11, after the shaft 6B has been moved into engagement with the stop 62, pivotally moves the latch arm to the right to cause the lug to move out of the retaining groove 73. When the lug 'l0 is free of the groove 13 the arm is moved downwardly to cause lugs 64 and 66 to engage and lock the arms 22 and 26 against relative angular movement. It will also be noted that the engagement between the lugs 74 and 16 also limits the angular movement of the latch arm in a clockwise direction. When the plunger'44 is moved in the opposite direction the arm 58 is pivotally moved upwardly to disengage lugs 64 and 66. This counter-clockwise movement of the arm aligns the lugs 'l0 with the semi-circular guide grooves 13 and brings the stop 7i into engagement with the shaft 23. Continued retracting movement of the plunger simultaneously causes the lugs 10 to enter the grooves 'I3 and the upper and lower drag links to be moved from their longitudinally aligned positions to one in which they are disposed substantially parallel to one another.

Yoke arms 'i4 are secured to the extensions 16 of the lower portions of the latch member 58. Two pulleys 'I8 are provided on the outer eX- tremities of the yoke arms 'I4 which are set in longitudinal alignment with a pair of cables 82 each anchored at one end to a bracket 88 on a lower drag link, and at the other end passing over a pulley 84 mounted in a pulley bracket 86 which is attached to the corresponding upper drag link 26, and terminating in a cable end fitting 88. A double tension spring 96 is interposed between each fitting 88 and a terminal link 92 which is secured to the corresponding extension arm 46 on an upper break link 26. As shown in FiguresV 4 and 5 the pulleys 'I8 on the ends of the yoke arms 14 ride on the cable 82 which is in tension and since the yoke arms are attached to the lower portion of the safety latch member 58 the latch member is constantlyV and resiliently. urged toward a locking position. Also the links 22 and 26 are constantly urged toward their fully extended .position of longitudinal alignment .by the cable :82 except when the pulleys :1.8 .are positionedfabove theaxial line of the lower break linksduring the latter portion ofthe retractive movementcr the earlier portion of the extension movement. While vpulleys 'I8 areso positioned, thereis a small incidental resultant force of the bungee acting to urge the links toward their fully retractedposition. Also, while the pulleys 18 are so.positioned,^there is no further elongation of the springs v6|), making it possible to use smaller, lighter .weight springs than otherwise would be the case.

:As shown in Figures 4, 5, 6 and 7, the'shock strut 1,0 strikes a door operating yoke 94 in its upward swing during retraction. The door operating yoke is provided with a rest pad 96 and two padded locking arms 98 and |00 centrally piilotedto the inner faces of the yoke arms on longitudinally disposed axes at .i 82 and |04 respectively. The locking arms 98 and |00 are each provided with a `notch |06 which receives an angled end |08 of the corresponding links |;|.8 and `|l2 which are .pivoted at ||4 and ||6 to vthe :extremities of the yoke arms and held in .lockedlposition in the notches |06 by springs The opposite end of the .links ||0 and 2 are-pivoted at ||8.and,l20 to levers |22 and |24 rigidlycarried by toroue tubes |26 and |28. The torque tubes run parallel to the fore and aft axis of `rnacelle structure 93 and are rotatably mounted von the innerfrarne structure of the nacelle by suitablebrackets-IS, |32. |34 and |36. The rear nacelledoors 38 and |40 are motivated by means of adjustable'rods .|42 and |44 which are pivoted at oneof their ends to the doors and at their other ends to levers |46 and |48 whichY are rigidly secured to the torque tubes |20 and |28. The frontnacelle doors |58 and l52 are motivated by similar adjustable rods |54 and |56 which are pivoted at one of their ends to the nacelle doors and at their other ends to leversV |62 and |64 fixed to the torque tubes |26 and |28. The center nacelle door |66 is not connected to the door retracting mechanism but is fixed to the shock strut |0 and is moved into a closed relationship with the other nacelle doors when the landing gear is fully retracted as shownl in Figure 8,

The inner retractin g links 38 are provided with passages as shown in Figure '12 which conduct uid to the hydraulic cylinder 42. Fluid may ow from a fluid line leading from the selector control valve through a port |68 thence through a'passage |10 in one of the links 38, into a shaft passage |12, and thence through a port |74 on the-.end of the cylinder L32. Simultaneously fluid from the opposite end of the cylinder 42 flows through a hose 16, into a shaft passage |18, througha passage |80 in the other link 38 and exhausts at |82 into a fluid line leading to the selector-control valve. In retraction of the gear, the flow as outlined above is reversed so that fluid is directed through the port |82 and passes into the vfrontend ofthe cylinder causing the piston to retract. The port |68 then becomes the exhaust opening for uid trapped in the upper portion` of the cylinder.

In operation, when the landing gear is to be retractedinto the nacelle, hydraulic fluid is admitted to the inlet tube |82. From this point fluidpasses through one of the inner retractipg links .38 into the hose |16 and directly into the Quterend portion of the cylinder 42, The piston .43 therein and the piston plunger 44 move inwardly pulling the latchmember 58 4upwardly 6.. against the action of the bungeezcable` 82'therehy dislodginglthe stop lugs 66 from theastop lugs 64. The guide lugs l0 are then in a position to be received byv the semi-circular guide .grooves 13. Continued movement lof thenplunger 44 pulls on the ilatch arm 58, the finger '1| of which bears against the shaft 28 and which therefore is now mechanically a xed part of the arm 4,6 of the link26. .The force thus applied to the link 26 laterally of its longitudinal axis breaksthe upper and lower links 22 and 26 about the shaft .28 which fold `about themselves between the pivot shaft 30 on theinner airplane structure and the pivot shaft 24onthe shock strut I0.

The outer retracting links 32 are pivoted at the shaft -34 to the `upper drag links 26 and attheir other ends at the shaft 36 to the hydraulic cylinder- 42 and the-inner retracting links 38. The leverage of lthis linkage is such that the hydraulic cylinder is at all points of rotation placed innan advantageous operating position for up ordown movement of the landing gear, the shaft 3,6 moving in a path which is at all times substantially displaced from the links 26. The median section of 'this path is at a greater displacement'from the links 26 than the ends thereof, giving the hydraulic jack the greatest mechanical advantage when the load value is the highest due to the relatively more nearly vertical movement of the wheels and the greater air 'resistance corresponding to this median section ofthe path of shaft 36. The leverage of the linkage is also such as to place upon the hydraulic jack a light load when the gear is fully retracted enabling the jack to relatively easily hold the gear in retracted position.

As the drag links continue to fold and the landing gear is drawn into the nacelle the shock strut I0 engages the door operating yoke. The first contact of the strut in the yoke is against the two locking levers 98 and |00. This movement disengages the links ||0 and H2 and as the yoke continues to move upward levers |22 and |24 turn torque tubes |26 and |28. The levers |46, |48. |62 and |64 are moved by the torque tubes to pull their respectively associated adiustable rods upward, drawing with them the doors attachedthereto. Simultaneously the door |66 secured to the main strut moves into position between forward doors |58 |52 and aft doors |38 and |48 to completely close the landing gear compartment in the nacelle and present a streamlined aerodynamically clean surface to the ambient air stream. The gear is held in the nacelle hy a `latch l(not shown) which automatically engages a catch on the aircraft frame structure. This latch is released by thepilot at the beginning of the extension movement of the gear.

When the landing gear is being extended the force of the passing air stream cooperates with the force of the hydraulic jack and with gravity to move the gear to its nal landing position. Both the main strut and drag strut move with the air stream and the articulated ends of the links of the drag strut also have a folding movement in the same direction as the air stream. The bungee cable applies an additional forceto effect the gear extending movement. Should the hydraulic jack fail, the gear may be extended by releasing the latch by which it is secured to the aircraft structureand allowing gravity, the wind load and the action of the bungee cable to move the gear to its extended position.

When the gear reaches fully extended position, itis'automatically locked against any retracting movement by a substantial, effective and positive lockingV device which is constantly readied for locking action by the bungee cable and held securely in locking position by this cable after the fully extended position is reached.

It will be observed from Figures 3 and 5 that with the landing gear in retracted position the links and hydraulic jack ofthe retracting linkage are. disposed substantially within the cylindrical space between the two wheels of the landing gear. Full advantage is thus taken of the spatial economy gained by using two wheels instead of one on the main oleo strut. f

The landing gear described herein andillustrated in the accompanying drawings embodies our invention. Other landing gears may also embody the invention as to one or more or all of its features. The invention is not limited to the landing gear herein described or to any other particular landing gear but is defined in the appended claims.

We claim: g

1. In an aircraft landinggear, the combination of ra pair of articulated break links longitudinally aligned in the gear extended position and foldable in theA gear retracted position; aV locking member xed to one of said links; a locking member p iVotally mounted on and movable with the other of said links, said last named locking member 4cooperative when engaged with Ythe first named locking member to hold the links against relative angular movement; means carried by the other of said links for positively holding said pivotally mounted locking member out of engagement with said first named locking member except when the links are in the fully. extended position; and resilient means acting upon the ivotally mounted locking member in all positions of the break links in a manner tending to pivotallyrmove said locking member into engagement with said rst named locking member so that said pivotally mounted member is moved into engagement with the said rst named lockingmember upon release thereof by said holding means. p

2. In an aircraft landing gear, the combination of: a pair of articulated break links longitudinally aligned in the gear extended position and foldable in the gear retracted position; a lug fixed to one of said links; a latch arm pivotally mounted on and movable with the other of said links; a lug carried by said latch arm-and cooperating with the iirst named lug when engaged therewith to hold the links against relative angular movement; means carried by the other of said links for guiding movement of said arm and for holding said latch arm out of a position in which the lug carried thereby can engage with the first named lug except when the links are in fully extended positions; and resilient means acting upon the latch arm and normally tending to move the latch arm into a position in which the lug carried thereby is engaged with the first named lug so that said pivotally mounted member is moved' position when the gear'isextended to a foldedv position when the gear is retracted; means for moving said links between said positions; a pulley mounted on one of said links offset from the longitudinal axes of the links when aligned and adjacent the articulating axis; an arm carried by the other of said links adjacent the end thereof; a second pulley carried by said arm; a resiliently extensible strand connected at one end to one of said links and running over the rst named pulley and reversely extending about the other of said pulleys; and means for connecting the free end of said strand to the other of said links.

4. The combination dened in claim 2 in which said latch arm is pivoted to said other link on an axis radially displaced from the articulating pivot on the side opposite the folding side of said link, and in which said holding means holds said latch arm in a fixed position relative to said other link, and in addition thereto; means for apply-` ing a force to said arm in one direction when said arm is in said one radial position to move it to said fixed position and thereafter fold said links and for applying a force to said arm in the` other direction when said links are in folded position to move said links to extended position and thereafter move said arm to said one radial position.

5. In an aircraft landing gear, the combination of a main landing gear strut; means for pivotally mounting said strut on the frame structure of the aircraft; a drag strut secured to the frame structure for moving said main strut to landing and retracted positions, comprising'two articulated addition thereto; a resilient means for applying a force to said latch arm tending to move it to locking position.

7. In an articulation locking device for the drag links of an airplane landing gear, the combination of: an offset first arm at the articulated end of one link extending laterally therefrom opposite the folding side of said link; a similar second arm similarly positioned on the other link; a latch pivoted to the rst arm; a cylindrical stop for said latch centered on the axis of articulation; an arcuately shaped, locking, first lug on the second arm, the arc being centered about said axis when the links are in extended position; a mating arcuate second lug on the latch, concentrically beyond said first lug and equidistant therewith from said axis when said latch is in locking position, said lugs being in locking position when said latch is spaced from said cylindrical stop and being unequally spacedV from said axis in release position whenY said latch is against said cylindrical stop; a lug on said latch proximate said cylindrical stop when said latch engages said stop; an arcuate guideway means for said lug on said other link, centered about said axis and beginning at a point proximately clearing said lug when said latch engages saidcylindrical stop and said arms are in extended position, and extending around said axis on the side toward said arms; and means for moving said latch between said locking position and said release position. v

' 8:. .The-z combination .deiinedzxinz` claim 3 'and lin addition; thereto aalockinggf device on said. links for locking i. the linksfirr aligned;` position;` said strand beingconnected'to.resiliently apply aV force acting tomove thelocking device to'locking position; and meanszfor preventing` said movement to locking,` position;exceptzwhensaid links `are in aligned positionl..

9. The combination defined in claimn133' in which said..` mounting means comprises a link hinged1atoneendto.lthetframe structure adjacently above the hinge of the upper link and hinged at the other end to the other end of the jack and comprises another link hinged at one end to the other end of the jack and hinged at the other end to the upper link to the frame structure, and in which said articulated links are inclined upwardly at a substantial angle atretraction:

In an" aircraft havingag-.landingf-:gear-enclosing chambenmthe combination of: a main landing gear strut connected to the airplane to be retracted within saidv enclosure in a position extending longitudinally of the plane; a vertically movable transverseyokezinlthe chamber disposed to befmovedupwardly'by said strut as it moves intosaidchamber; closing :doors `for said chamber;` motion transmitting/means connecting the yoke and doors for closing the doors upon upward movement of said yoke; and means on said yoke for locking said motion transmitting means in door opening position when said yoke and strut are disengaged and for gripping said strut against vertical play with respect to said yoke and simultaneously unlocking said motion-transmitting means in response to vertical pressure between said strut and yoke. l

1l. The combination defined in claim 10 in which the said door locking and yoke gripping means comprises a pair of bell crank levers hinged to the legs respectively of said yoke approximately at the level of the yoke axis, comprises lugs on the end of said levers, the two upper lugs being contacted and spread apart by the upwardly moving strut to move the lower lugs into gripping contact with the under side of the strut and further comprises latching means on thelevers and detent means on the motion-transmitting means, the latching means engaging the detent means when the levers are in positions corresponding to disengagement of the yoke and strut and the latching means disengaging the detent means in response to pressural engagement of the yoke and strut.

12. In an aircraft landing gear, the combination of: a pair of articulated break links longitut dinally aligned in the gear extended position and foldable in the gear retracted position; a, lug fixed to one of said links; a latch arm pivotally mounted on and movable with the other of said links; a guiding lug carried by said arm; a latching lug carried by said latch arm andmcooperating with the rst named lug when engaged therewith to hold the links against relative angular movement; means carried by the other of said links and engaging said guiding lug and holding said latch arm against pivotal movement relative to the link to which it is pivotally mounted until said links are moved to the fully extended position; and resilient means acting upon the latch and normally tending to move the latch arm into a position in which the lug carried `thereby is engaged with the rst named lug.

13. In an aircraft landing gear, the combination of: a main landing gear strut; means for 10 pivotally mounting said strut onv the frame struc.. ture `of an aircraft; aldrag strutfor moving said` main strut to; landingand. retracted positions, comprising two articulated links, the upper link being hingedto saidframe structure andthe wardly` oisetf from:` said r upper" link duringr the movement of said. articulated 4links/whereby the mechanical advantage: of thefjack isrsubstantially constant.4 throughoutv the entirer range .off movement ofr said .upper link.

141 In an aircraft` landingifgear; the r`combina; tion of a landing gear strut; meansA forpivotally mountingthe upper-end :of said strut on; the frame structure ofi an` aircraft; a hydraulicpijack; means forpivotally securing `onegendfofisaid'jack tothe lowerrendportion of saidystrut'fonmovement about `an axis: adjacentv the lower: end .of

said strut; ag pair of articulatedisupportzlinks;

means for pivotally securing the free ends of said links to said frame structure and the end of said strut adjacent the pivotally mounting means respectively; means for pivotally supporting the other end of said jack for movement about the articulation axis of said support links whereby the last named end of said jack moves in an arcuate path outwardly oiset from said strut during movement of said landing gear, thereby maintaining the mechanical advantage of the jack substantially constant throughout the entire range of movement of said landing gear during extension and retraction thereof.

15. In an aircraft landing gear, the combination of: a landing gear strut; means for pivotally mounting the upper end of said strut on the frame structure of an aircraft; a hydraulic jack; means for pivotally securing one end of said jack to the lower end portion of said strut for movement about an axis adjacent the lower end of said strut; a pair of supporting links; pivot means for connecting an end of one of said supporting links to an end of the other of said links, the free end of said jack being secured to said pivot means; means for pivotally securing the free end of one of said supporting links to said frame structure; and means for pivotally securing the free end of the other of said supporting links to said strut so that said pivot means and the end of the jack secured thereto is displaced from said strut thereby ef.. fecting a substantially constant lever arm on which the force developed by said jack is exerted throughout substantially the entire cycle of retraction and extension of said landing gear.

16. In an aircraft landing gear, the combination of a landing gear strut; means for pivotally mounting the upper end of said strut on the frame structure of an aircraft; a hydraulic jack; means for pivotally securing one end of said jack to the lower end portion of said strut for movement about an axis adjacent the lower end of said strut; a pair of supporting links; pivot means for connecting an end of one of said supporting links to an end of the other of said links, the free end of said jack being secured to said pivot means; means for pivotally securing the free end of one of said supporting links to saidrfram'e structure; and means for pivotally securing .the free end of the other of said supporting links to said strut so that said pivot means and the end of the jack secured thereto is displaced a substantial distance from' said strut and movable in an arcuate path relative to said frame structure during movement of said landing gear whereby the mechanical advantage of said jack is substantially constant throughout substantially the entire cycle of retraction and extension of said landing gear.

17. In an aircraft landing gear, the combination of: a landing gear strut; means for pivotally mounting the upper end of said strut on the frame structure of an aircraft; a hydraulic jack pivotally secured at one end to the lower end portion of said strut on an axis adjacent the lower end thereof; a pair of supporting links; pivot means for connecting an end of one of Said supporting links to an end of the other of said links; means for pivotally securing the free end of one of said supporting links to said frame structure at a point spaced from the pivotal connection between said frame structure and said strut; and means for pivotally securing the free end of the other of said supporting links to said strut so that said pivot means interconnecting said supporting links is moved during movement of said strut in an arcuate path relative to thek frame structure, the free end of said jack being secured to said pivot means so that the Aend of the jack is displaced from the strut thereby effecting a lever arm on which the force developed by said jack is exerted during substantially the entire cycle of retraction and extension of said landing gear.

CHARLES S. GLASGOW.

EDWARD F. BURTON.

REFERENCES CITED The following references are of record in the 526,353 Great Britain Sept. 17, 1940 

